The present invention relates to a process for preparing post-crosslinked polymer bead whose surface area and pore volume are increased, more specifically, to a method for controlling surface area and pore volume of polymer bead by post-crosslinking gel-type copolymer bead whose crosslinking degree is low and surface area is small, or macroporous-type copolymer bead whose crosslinking degree is high and surface area is intermediate in the presence of a Friedel-Crafts catalyst, a process for preparing post-crosslinked polymer bead with increased surface area and pore volume, and sufficient pore size allowing the separation of organic compounds, and polymer beads produced thereby.
Various kinds of toxic compounds contained in the industrial waste water have been generated, as the industrialization progresses. Naturally, a method for removing or recovering the toxic organic compounds has been required in the art. Even though highly selective chromatographic adsorbents and separatory membranes have gained wide acceptance among the users, needs have continued to exist for the development of a material which possesses better separation power for organic compounds than conventional adsorbents. In particular, efficient means for separating biologically active materials and proteins have been explored as the biotechnology develops rapidly.
Polymeric adsorbents employed in that purpose include two types of commercially available adsorbent resins, i.e., porogen-modified styrene/divinylbenzene adsorbents and methylene-bridged styrene/divinylbenzene adsorbents.
Porogen- or diluent-modified styrene/divinylbenzene adsorbent which is collectively referred to as macroporous resin, porogens such as toluene, isooctane, and amylalcohol are added to control the pore size in the course of polymerization, whereby relatively large pore size can be formed. Crosslinking monomer of divinylbenzene ranging from 0.35 to 0.80 by weight fraction is employed to the polymerization, to give stabilization and rigidity to the polymer structure while preventing pore collapse due to large pore size. However, it has revealed a critical problem that polymer beads with increased surface area and high porosity for separator purposes cannot be easily obtained by the afore-mentioned method.
On the other hand, the methylene-bridged styrene/divinylbenzene adsorbents, are prepared from lightly crosslinked gel or macroporous polymers, whose crosslinking degree is typically less than 0.08 weight fraction. The polymers possess good swelling characteristics, and undergo considerable expansion during methylene-bridging process, which endows the adsorbents with large surface area. Accordingly, the polymeric adsorbents provide a high adsorption capacity associated with large surface area, while maintaining low adsorption kinetics associated with microporosity.
As fully described above, the porogen-modified styrene/divinybenzene adsorbents provide a high level of macroporosity and relatively small surface area, thus show desirable adsorption kinetics but low adsorption capacity, while the methylene-bridged styrene/divinylbenzene adsorbents have drawbacks of low adsorption kinetics due to the microporosity. Thus, it would be desirable to combine the advantages of high adsorption capacity and kinetics in a single polymeric adsorbent, by controlling critical parameters to determine the surface area and pore volume.
U.S. Pat. No. 5,416,124 describes a process for preparing polymeric adsorbents with increased surface area and pore volume which comprises the steps of: i) preparing crosslinked copolymer beads, ii) halogenation of the copolymer beads, and iii) post-crosslinking the halogenated copolymer beads. However, the process is less satisfactory in a sense that formation of pore and increment of surface area are carried out simultaneously, preventing polymer beads from easy control of pore size.
Further, a method for increasing surface area by post-crosslinking styrene/divinylbenzene coplymer with crosslinking agent such as chloromethyl ether and chloroethyl ether in the presence of a Friedel-Crafts catalyst has been proposed in the art. However, pore size control and large surface area cannot be realized, since the pore formation and surface area increment are also performed in a simultaneous manner.
Under the circumstances, there are strong reasons for exploring and developing a novel process for preparing polymer beads by separating the steps of forming pore structure and expanding surface area to control pore size.
The present inventors have made an effort to solve the problems of the prior processes, and prepared polymer beads with increased surface area and pore volume by polymerizing a suspension of organic phase in an aqueous phase to prepare copolymer beads having chloromethy groups with suitable pore structure(mesoporosity and macroporosity) associated with adsorption kinetics, and post-crosslinking the copolymer beads in a swollen state in the presence of a Friedel-Crafts catalyst.
A primary object of the present invention is, therefore, to provide a method for controlling surface area and pore volume in polymer beads to improve adsorption capacity and adsorption kinetics.
The other object of the invention is to provide a process for preparing polymer beads whose surface area and pore volume are increased.
Another object of the invention is to provide polymer beads with increased surface area and pore volume.